This invention relates to a machine for producing perforated plastic sheets used to package various types of foods, especially produce, and more particularly, to a machine which receives a continuous roll or web of flexible plastic material and perforates it at spaced intervals, cuts the roll into individual sheets, each having perforations, and then stacks the sheets into a receptacle for shipment.
It has been found desirable to package articles of produce requiring ventilation, such as berries, grapes, cherries, lettuce and the like, in a thin flexible plastic film or sheet material which is formed into separate sheets, each having a slit pattern capable of expanding around the produce for wrapping or bagging it. As discussed in detail in U.S. Pat. No. 3,958,751, the split pattern formed in the individual plastic sheets greatly expands when produce is placed therein, forming, in effect, a bag which wraps around and contains the produce. The openings created in the expanded slit pattern provide for ventilation and application of water to the contents to keep it fresh, as well as facilitating viewing and touching of the article without damage to or removal of the contents.
Accordingly, several machines have been developed which produce individual sheets of flexible plastic film material having an expansible slit pattern for receiving produce as described above. In general, these machines are designed to receive a continuous length of plastic material from such as a roll or web. The plastic is first perforated with the desired slitted pattern at spaced intervals, and a cutting means is then employed to cut the length of plastic into individual sheets, each having a slitted pattern. Finally, the sheets are transferred to a position for stacking by conveyer means where they are placed into receptacles for shipment.
A major problem encountered in the operation of many prior art machines described above, is caused by the diaphanous character of the plastic film or sheet material used for the packaging wrap. The plastic material used is very thin and flexible, so that it may expand sufficiently to wrap around produce of varying sizes. However, particularly at higher temperatures and humidity such as during the summer months, extreme difficulty has been encountered in manipulating and handling the material throughout the perforating, cutting, transfer, and stacking operations described more fully below. One of the most critical phases in the operation of this type of machine is the movement of the individual sheets after they have been cut from the continuous roll, to a conveyer means for transfer to the stacking point. It has been found in using most prior art machines, that the sheets frequently jam or bunch up at the beginning of the conveyer means, causing costly delays while the material is removed. The efficiency of such machines are thus greatly reduced, and the rate of production suffers. Additionally, such machines usually require manual stacking of the sheets in receptacles for shipment as they are transferred to the stacking position. It has also been found that the cutting means of most prior art machines, consisting of a rigid blade, is quickly dulled and must be replaced frequently which further reduces the efficiency of such machines.